Ireland's Paddy Power also offered short odds on the three, as well as long odds on unlikely candidates - including U2 singer Bono at 1,000/1. It also offered 1,000/1 odds on Father Dougal Maguire, the simpleminded fictional priest from 1990s U.K. sitcom "Father Ted."

Professor Chester Gillis, a theology professor at Georgetown University and the dean of Georgetown College, told "CBS This Morning," that the church may choose a cardinal of a less "advanced age" and that while the possibility is "remote," Cardinal Timothy Dolan, archbishop of New York, could be a candidate.

The timing of Pope Benedict's surprise announcement, coming days before the beginning of Lent - the 40 day period before Easter, the most important feast in the Catholic Church - presents a challenge to church officials who would like a new pope in place by March 24, the beginning of Holy Week.